This study is part of a series of projects to develop and test new vaccines for meningitis. Previously researchers have given nose drops containing N. lactamica to over 350 volunteers, and shown that many of them (35-60%) can become colonised with N. lactamica and become resistant to becoming colonised with N.meningitidis without causing any illness or disease. In the future the study team would like to find out how N.lactamica helps children resist N.meningitidis, and develop new vaccines that exploit that mechanism.

In this pilot research, the research team will develop and validate a modification of the methodology previously used in another UK-based human challenge experiments. The research to be conducted in this study will inform the study team whether intranasal inoculation of reconstituted lyophilised Nlac (hereafter, lyoNlac), can result in immunising colonisation of participants and the optimal dose to achieve this.

Previous challenges have been conducted using frozen stocks of Nlac but this is relatively unsatisfactory because of instability of frozen stocks, and will not be practical in Mali. The facility to reconstitute dry powdered lyoNlac into water and inoculate as a nose drop will greatly simplify the experimental method. However, it is not known whether lyoNlac can be inoculated directly into volunteers and induce successful colonisation.

In summary this is a pilot study of the safety, efficacy and immunogenicity of the intranasal inoculation of healthy human volunteers with lyoNlac. This study will determine the efficacy of lyoNlac as an agent for inducing nasopharyngeal colonisation with this organism, which is an important methodological development for ease of administration of Nlac in experimental human challenge studies. The study team will aim to determine the dose of inoculum required to induce colonisation in 80% of volunteers (the Standard Inoculum or SI). This SI will be used in future studies aiming to optimise duration of colonisation and immunogenicity induced by lyoNlac.

Inclusion Criteria:

• Healthy adults aged 18 to 45 years inclusive on the day of enrolment
• Fully conversant in the English language
• Able and willing (in the investigator's opinion) to comply with all study requirements
• Provide written informed consent to participate in the trial
• For females only, willingness to practice continuous effective contraception (see below) during the study and a negative pregnancy test on the day(s) of screening and inoculation
• TOPS registration completed and no conflict found

Exclusion Criteria:

• Current active smokers defined as having smoked a cigarette or cigar in the last four weeks
• N. lactamica or N. meningitidis detected on throat swab or nasal wash taken at screening
• Individuals who have a current infection at the time of inoculation
• Individuals who have been involved in other clinical trials involving receipt of an investigational product over the last 12 weeks or if there is planned use of an investigational product during the study period
• Individuals who have previously been involved in clinical trials investigating meningococcal vaccines or experimental challenge with N. lactamica
• Use of systemic antibiotics within the period 30 days prior to the challenge
• Any confirmed or suspected immunosuppressive or immune-deficient state, including HIV infection; asplenia; recurrent, severe infections and chronic (more than 14 days) immunosuppressant medication within the past 6 months (topical steroids are allowed)
• Use of immunoglobulins or blood products within 3 months prior to enrolment.
• History of allergic disease or reactions likely to be exacerbated by any component of the inoculum, specifically soya.
• Contraindications to the use of ciprofloxacin, specifically a history of epilepsy, prolonged QT interval, hypersensitivity to quinolones or a history of tendon disorders related to quinolone use
• Any clinically significant abnormal finding on clinical examination or screening investigations
• Any other significant disease, disorder, or finding which may significantly increase the risk to the volunteer because of participation in the study, affect the ability of the volunteer to participate in the study or impair interpretation of the study data, for example recent surgery to the nasopharynx
• Occupational, household or intimate contact with immunosuppressed persons
• Pregnancy or lactation